Biocompatible magnetic nanocrystal, powder of a biocompatible magnetic nanocrystal bearing a surface reactive group and preparations thereof

Abstract

This invention is concerned with biocompatible magnetic nanocrystals highly soluble and dispersible in a physiological buffer, powder of biocompatible magnetic nanocrystals and nanocrystals bearing surface reactive N-hydroxysuccinimide ester moiety, and preparations thereof. The magnetic nanocrystals in powder form are highly soluble in a physiological buffer. The resultant aqueous colloidal solution presents long term stability in ambient conditions. Moreover, the carboxyl group on the surface of the magnetic nanocrystals can be converted to N-hydroxysuccinimide ester moiety in an organic solvent. The resultant powder of the magnetic nanocrystals carrying surface N-hydroxysuccinimide ester moiety is soluble and dispersible in an aqueous solution. Different types of biomolecules bearing amino group can covalently be attached to the magnetic nanocrystal simply by mixing them in aqueous solutions. Moreover, the powder of the magnetic nanocrystals bearing surface N-hydroxysuccinimide ester moiety retain reaction activity with biomolecule after long-term storage.

1. A powder of a biocompatible magnetic nanocrystal bearing a surface reactive N-hydroxysuccinimide ester moiety, wherein the surface of said biocompatible magnetic nanocrystal is bonded with a biocompatible macromolecule and an alkyl-containing molecule simultaneously, wherein said biocompatible macromolecule bonded on the surface of said magnetic nanocrystal has one or more carboxyl groups for further covalently conjugating the magnetic nanocrystal to a biomolecule, and wherein said surface reactive N-hydroxysuccinimide ester moiety is obtained by converting said surface carboxyl group on the biocompatible macromolecule to a N-hydroxysuccinimide ester moiety. 
     
     
       2. The biocompatible magnetic nanocrystal powder as claimed in  claim 1 , wherein said magnetic nanocrystal, after being stored for one year in powder form, still retains reactivity with a biomolecule bearing amino group. 
     
     
       3. A method for preparing the powder of a biocompatible magnetic nanocrystal bearing a surface reactive N-hydroxysuccinimide ester moiety as claimed in  claim 1 , comprising the following steps:
 1) introducing an organic solution of N-hydroxysuccinimide (NHS) followed by an organic solution of dicyclohexylcarbodiimide (DCC) or N,N-diisopropylcarbodiimide (DIC) into an organic solution of a biocompatible magnetic nanocrystal, wherein the surface of said biocompatible magnetic nanocrystal is bonded with a biocompatible macromolecule and an alkyl-containing molecule simultaneously, or a biocompatible macromolecule alone, wherein said biocompatible macromolecule bonded on the surface of said magnetic nanocrystal has one or more carboxyl groups for further covalently conjugating the magnetic nanocrystal to a biomolecule, to activate the surface carboxyl group on the magnetic nanocrystal at room temperature for 40 minutes-18 hours or at 4° C. for 2 hours-24 hours, wherein the molar ratio between the magnetic nanocrystal and dicyclohexylcarbodiimide or the molar ratio between the magnetic nanocrystal and N,N-diisopropylcarbodiimide ranges from 1:2 to 1:2000, and the molar ratio between dicyclohexylcarbodiimide and N-hydroxysuccinimide or between N,N-diisopropylcarbodiimide and N-hydroxysuccinimide ranges from 1:0.9 to 1:10; or 
 introducing the organic solution of dicyclohexylcarbodiimide or N,N-diisopropylcarbodiimide dropwise into an organic solution containing both the magnetic nanocrystal bearing a surface carboxyl group, and N-hydroxysuccinimide, to activate the surface carboxyl group on the magnetic nanocrystal at room temperature for 40 minutes-18 hours or at 4° C. for 2 hours-24 hours, wherein the molar ratio between the magnetic nanocrystal and dicyclohexylcarbodiimide or the molar ratio between the magnetic nanocrystal and N,N-diisopropylcarbodiimide ranges from 1:2 to 1:2000, and the molar ratio between dicyclohexylcarbodiimide and N-hydroxysuccinimide or the molar ratio between N,N-diisopropylcarbodiimide and N-hydroxysuccinimide ranges from 1:0.9 to 1:10; and 
 2) isolating the biocompatible magnetic nanocrystal bearing a surface reactive N-hydroxysuccinimide ester moiety from the reaction solution obtained in step (1) and removing the organic solvent, thereby obtaining a powder of the biocompatible magnetic nanocrystal bearing a surface reactive N-hydroxysuccinimide ester moiety. 
 
     
     
       4. The method as claimed in  claim 3 , wherein said isolating the biocompatible magnetic nanocrystal bearing a surface reactive N-hydroxysuccinimide ester moiety from the reaction solution comprises steps for centrifugating the resultant reaction solution and extracting the supernatant. 
     
     
       5. The method as claimed in  claim 3 , wherein said organic solvent is chosen from a group consisting of dichloromethane, trichloromethane, tetrahydrofuran, ethyl acetate, ethylene glycol dimethyl ether, 1,4-dioxane, pyridine, N,N-dimethylformamide, dimethyl sulfoxide or a mixture of any two of these solvents.